High voltage measurement system and calibration method

ABSTRACT

Voltage measurement calibration methods and junction circuits. In one embodiment, the junction circuit includes a capacitor and a voltage adjustment circuit. The junction circuit is electrically coupled to an output of a capacitive voltage divider circuit. The capacitor is electrically coupled between the output of the capacitive voltage divider circuit and a reference terminal. The voltage adjustment circuit is electrically coupled between the output of the capacitive voltage divider circuit and an output of the junction circuit. The voltage adjustment circuit includes an adjustable impedance component configured to adjust a voltage gain of the voltage adjustment circuit.

BACKGROUND

Voltage sensors are commonly used in high voltage monitoring systems. Insome cases (for example, in power distribution systems havingtransmission and distribution voltages from 2,400 volts to 100kilovolts), it is necessary to scale down high voltages so they can bemeasured.

SUMMARY

A voltage divider may be used to scale down high voltages so they can bemeasured by, for example, a voltmeter. In some cases, a voltage dividermay be included within a voltage sensor and may be implemented usingcomponents of an electrical device (for example, switchgear in a powerdistribution system). The voltage ratio of a voltage divider representsthe ratio between the magnitude of output signals and the magnitude ofinput signals. Voltage ratios of passive (non-power consuming) voltagedividers may vary due to process variations of the components used.Existing voltage measurement systems that use passive voltage sensorsaccount for varying voltage ratios by applying a digital “ratiocorrection factor” (RCF) to voltage readings. A ratio correction factoris unique to a particular voltage sensor system and must be programmedinto an associated meter or control to which it is wired. Such ratiocorrection factors may undesirable from an end user perspective becausethey are unique to particular voltage sensor systems and if one or morecomponents of the voltage sensor system are replaced, the associatedratio correction factor must also be changed in a meter or controllerthat determines voltage from the voltage sensor system. For example, acontroller may need to be re-programmed with an updated ratio correctionfactor for a new voltage sensor. This programming task may be difficultfor the end user to perform. For example, in some instances differentgroups of individuals perform the equipment installations in the fieldand the controller programing tasks. Thus, re-programming may requirecoordination between at least the two groups. Additionally, theprogramming task may require user access to proprietary software andspecial programming cables.

Some embodiments provide, among other things, a junction circuit that iselectrically coupled to an output of a capacitive voltage dividercircuit. In one embodiment, the junction circuit includes a capacitorand a voltage adjustment circuit. The capacitor is electrically coupledbetween the output of the capacitive voltage divider circuit and areference terminal. The voltage adjustment circuit is electricallycoupled between the output of the capacitive voltage divider circuit andan output of the junction circuit. The voltage adjustment circuitincludes an adjustable impedance component configured to adjust avoltage gain of the voltage adjustment circuit.

Another embodiment provides a switchgear system. In one example, theswitchgear system includes a switchgear device, a voltage dividercircuit, and a junction circuit. The voltage divider circuit includes anoutput and an input electrically coupled to the switchgear. The junctioncircuit includes an input, an output, and a voltage adjustment circuit.The input of the junction circuit is electrically coupled to the outputof the voltage divider circuit. The output of the junction circuit iselectrically coupleable to a voltage measurement device. The voltageadjustment circuit is configured to adjust a voltage gain of the voltagedivider circuit.

Another embodiment provides a method of calibrating a recloser voltagemeasurement system. In one example, the recloser voltage measurementsystem includes a voltage divider and a voltage adjustment circuit. Thevoltage divider is electrically coupled to a recloser. The voltageadjustment circuit is electrically coupled to an output of the voltagedivider. The method includes determining a first voltage measurement ata high voltage input to the recloser. The method also includesdetermining a second voltage measurement at an output of the voltageadjustment circuit. The method further includes calculating a differencebetween the first voltage measurement and the second voltagemeasurement. The method also includes determining a target voltage gainbased on the determined difference between the first voltage measurementand the second voltage measurement. The method further includesadjusting a voltage ratio of the voltage divider by setting the voltageadjustment circuit to the target voltage gain.

Other aspects and embodiments will become apparent by consideration ofthe detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a high voltage monitoring system, accordingto some embodiments.

FIG. 2 is a circuit diagram of a voltage measurement system, accordingto some embodiments.

FIG. 3 is a circuit diagram of a part of a voltage adjustment circuitwhose voltage gain is controlled by a dip-switch resistor array,according to some embodiments.

FIG. 4 is a circuit diagram of a part of a voltage adjustment circuitwhose voltage gain is controlled by a digital potentiometer, accordingto some embodiments.

FIG. 5 is a diagram of a switchgear system including a recloser, acontrol cable, and a recloser controller, according to some embodiments.

FIG. 6 is a diagram of a voltage sensor, according to some embodiments.

FIG. 7 is a block diagram of a recloser controller, according to someembodiments.

FIG. 8 is a diagram of a switchgear system for a recloser voltagemeasurement system, according to some embodiments.

FIG. 9 is a flow chart of a method for calibrating a recloser voltagemeasurement system, according to some embodiments.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of a monitoring system 100 for measuringvoltage at a high voltage electrode 105, according to some embodiments.The high voltage electrode 105 may be electrically coupled to highvoltage source, for example, a transmission or distribution line. Themonitoring system 100 in FIG. 1 includes a voltmeter 110 which cannotdirectly measure high voltage from the high voltage electrode 105. Thus,a voltage sensor 115 (including a voltage divider) is electricallycoupled to the high voltage electrode 105 to scale down the high voltageto a lower voltage that can be measured by the voltmeter 110. For safetyor practical reasons, the voltmeter 110 may be located a distance awayfrom the high voltage electrode 105 and the voltage sensor 115. Thus,the voltmeter 110 is electrically coupled to the high voltage electrode105 and the voltage sensor 115 via a control cable 120. A junction board125 (located near the voltage sensor 115) is used to electrically couplethe voltage sensor 115 to the control cable 120.

As described above, the high voltage is scaled down via a voltagedivider included in the high voltage electrode 105 and the voltagesensor 115. The voltage divider may be designed to measure a specifiedlow voltage output for a specified high voltage input. For example, ahigh voltage input of 10 kilovolts could ideally yield a sensed lowvoltage output of 1 volt, for a voltage ratio of 10,000 to 1. However,due to variations in the physical layout and electrical characteristicsof passive components included in the voltage divider, a unique ratiocorrection factor must be determined for each voltage sensor to scalethe output for an accurate reading. In earlier systems, the voltagesensor 115 is tested with a high voltage input to determine a ratiocorrection factor based on the ratio of applied input to measuredoutput. The ratio correction factor is provided to an end user who mustprogram the ratio correction factor into the voltage measurement deviceto make the corrections. However, this prior technique presents problemsfor an end user. Among other problems, each time a component of themonitoring system 100 is replaced, a new ratio correction factor must beprogrammed into the voltmeter 110. This process requires programmingexpertise and additional equipment in the field that may not be readilyavailable or possible to perform due to safety concerns or practicallimitations.

FIG. 2 is a circuit diagram of a voltage measurement system 200 thateliminates the need for ratio correction factors programmed into acontroller, according to some embodiments. The voltage measurementsystem 200 in FIG. 2 includes a reference terminal 205, a high voltage(HV) line electrode 210, a voltage divider circuit 215, a junctioncircuit 220, and a voltage measurement circuit 225. In some embodiments,the reference terminal 205 is electrically coupled to earth ground.

The input of the voltage divider circuit 215 is electrically coupled tothe HV line electrode 210 and the reference terminal 205. In someembodiments, the voltage divider circuit 215 is included in a voltagesensor (for example, the voltage sensor 115 in FIG. 1). The voltagedivider circuit 215 in FIG. 2 includes a capacitor 230 (C1) electricallycoupled in series with another capacitor 235 (C2) to divide the voltagedrop across the HV line electrode 210 and the reference terminal 205 ata voltage screen electrode 240 (i.e., the output of the voltage dividercircuit 215).

The input of the junction circuit 220 is electrically coupled to theoutput of the voltage divider circuit 215. In some embodiments, thejunction circuit 220 is included in a junction board (for example, thejunction board 125 in FIG. 1). The junction circuit 220 includes acapacitor 245 (C3) electrically coupled between the reference terminal205 and the output of the voltage divider circuit 215 (i.e., the voltagescreen electrode 240). The capacitor 245 (C3) is electrically coupled inparallel with the capacitor 235 (C2) such that the capacitor 230 (C1),the capacitor 235 (C2), and the capacitor 245 (C3) together form acapacitive voltage divider network. Ideally, the transfer function H(also known as the voltage ratio) of this capacitive voltage dividernetwork is

H=C_1/(C_1+C_2+C_3)   (Equation 1)

where

-   -   C_1=capacitance of the capacitor 230 (C1),    -   C_2=capacitance of the capacitor 235 (C2), and    -   C_3=capacitance of the capacitor 245 (C3).

The junction circuit 220 also includes a voltage adjustment circuit 250electrically coupled in series with the capacitor 245 (C3) to adjust thevoltage ratio of the capacitive voltage divider network. The voltageadjustment circuit 250 adjusts the voltage ratio of the capacitivevoltage divider network by applying a voltage gain to the output of thecapacitive voltage divider network.

The voltage measurement circuit 225 is electrically coupled to theoutput of the junction circuit 220. In some embodiments, the voltagemeasurement circuit 225 is included in a voltmeter (for example, thevoltmeter 110 in FIG. 1). The voltage measurement circuit 225 in FIG. 2includes a control resistor 255 (R_Control) representing, for example,the resistance within a voltmeter used to measure the voltage dropacross the output of the voltage adjustment circuit 250 and thereference terminal 205.

As described above, the voltage adjustment circuit 250 in the junctioncircuit 220 adjusts the voltage ratio of the capacitive voltage dividernetwork by applying a voltage gain to the output of the capacitivevoltage divider network. In some embodiments, the voltage gain of thevoltage adjustment circuit 250 is controlled by an adjustable impedancecomponent. In some embodiments, the adjustable impedance component is adip-switch resistor array. For example, FIG. 3 is a circuit diagram of apart of a voltage adjustment circuit 300 whose voltage gain iscontrolled by a dip-switch resistor array 305, according to someembodiments. The voltage adjustment circuit 300 in FIG. 3 includes tworesistors 310 (R1) and 315 (R2) that are electrically coupled between aninput 317 and a reference terminal 320 to form a voltage divider.Ideally, the transfer function H of the voltage divider formed by theresistor 310 (R1) and the resistor 315 (R2) is

H=R_2/(R_1+R_2)   (Equation 2)

where

-   -   R_1=resistance of the resistor 310 (R1), and    -   R_2=resistance of the resistor 315 (R2).

The voltage adjustment circuit 300 in FIG. 3 also includes anoperational amplifier 325 whose voltage gain is controlled by thedip-switch resistor array 305. The dip-switch resistor array 305 in FIG.3 includes three resistors Rf1, Rf2, and Rf3 electrically coupled inseries with each other, and three dip switches SW1, SW2, and SW3electrically coupled in series with other. In alternate embodiments, thedip-switch resistor array 305 may include more or less resistors and/ormore or less dip switches. Each dip switch in the dip-switch resistorarray 305 is electrically coupled in parallel with an individualresistor. For example, the dip switch SW1 is electrically coupled isparallel with the resistor Rf1. When one of the dip switches is in aclosed positioned (i.e., ON), the resistance of the parallel-coupledresistor is not included in the total resistance across the dip-switchresistor array 305 (i.e., the dip switch shorts out the parallel-coupledresistor). For example, when the dip switch SW2 is in the closedposition, the resistance of the resistor Rf2 is not included in thetotal resistance across the dip-switch resistor array 305.Alternatively, when one of the dip switches is in an open position(i.e., OFF), the resistance of the parallel-coupled resistor is includedin the total resistance across the dip-switch resistor array 305. Forexample, when the dip switch SW2 is in the open position, the resistanceof the resistor Rf2 is included in the total resistance across thedip-switch resistor array 305. The total resistance across thedip-switch resistor array 305 (i.e., the feedback resistance of theoperational amplifier 325) is set based on the positions of the threedip switches SW1, SW2, and SW3. For example, when the dip switches SW1and SW2 are in the open position and the dip switch SW3 is in the closedposition, the total resistance across the dip-switch resistor array 305is equal to the sum of the resistances of the resistors Rf1 and Rf2. Asan additional example, when the dip switch SW2 is in the open positionand the dip switches SW1 and SW3 are in the closed position, the totalresistance across the dip-switch resistor array 305 is equal to theresistance of the resistor Rf2.

The operational amplifier 325 is configured as a non-inverting amplifierwith negative feedback. The negative feedback is provided via thedip-switch resistor array 305 and a resistor 330 (Rg) which together actas a voltage divider. The dip-switch resistor array 305 is electricallycoupled between the output and the inverting input of the operationalamplifier 325. The resistor 330 (Rg) is electrically coupled between theinverting input of the operational amplifier 325 and the referenceterminal 320. Ideally, the closed-loop gain A_CL of the operationalamplifier 325 is

A_CL=1+(R_f/R_g)   (Equation 3)

where

-   -   R_f=total resistance across the dip-switch resistor array 305,        and    -   R_g=resistance of the resistor 330 (Rg).

The non-inverting input of the operational amplifier 325 is electricallycoupled to the output of the voltage divider formed by the resistor 310(R1) and the resistor 315 (R2). The output of the operational amplifier325 is electrically coupled to an output 335 of the voltage adjustmentcircuit 300. Thus, by combining equations 2 and 3, the voltage gainV_Gain of the voltage adjustment circuit 300 is

V_Gain=V_Out/V_In=(R_2/[R_1+R_2])×(1+[R_J/R_g])   (Equation 4)

where

-   -   V_Out=voltage at the output 335 of the voltage adjustment        circuit 300,    -   V_In=voltage at the input 317 of the voltage adjustment circuit        300,    -   R_1=resistance of the resistor 310 (R1),    -   R_2=resistance of the resistor 315 (R2),    -   R_f=total resistance across the dip-switch resistor array 305,        and    -   R_g=resistance of the resistor 330 (Rg).

In alternate embodiments, the adjustable impedance component is adigital potentiometer. For example, FIG. 4 is a circuit diagram of avoltage adjustment circuit 400 whose voltage gain is controlled by adigital potentiometer 405 (Rg), according to some embodiments. Thevoltage adjustment circuit 400 in FIG. 4 includes two resistors 410 (R1)and 415 (R2) electrically coupled between an input 417 and a referenceterminal 420 to form a voltage divider. Ideally, the transfer function Hof the voltage divider formed by the resistor 410 (R1) and the resistor415 (R2) is

H=R_2/(R_1+R_2)   (Equation 5)

where

-   -   R_1=resistance of the resistor 410 (R1), and    -   R_2=resistance of the resistor 415 (R2).

The voltage adjustment circuit 400 in FIG. 4 also includes anoperational amplifier 425 whose voltage gain is controlled by thedigital potentiometer 405 (Rg). The operational amplifier 425 isconfigured as a non-inverting amplifier with negative feedback. Thenegative feedback is provided via the digital potentiometer 405 (Rg) anda resistor 430 (Rf) which together act as a voltage divider. The digitalpotentiometer 405 (Rg) is electrically coupled between the invertinginput of the operational amplifier 425 and the reference terminal 420.The resistor 430 (Rf) is electrically coupled between the output and theinverting input of the operational amplifier 425. Ideally, theclosed-loop gain A_CL of the operational amplifier 425 is

A_CL=1+(R_f/R_g)   (Equation 6)

where

-   -   R_f=resistance of the resistor 430 (Rf), and    -   R_g=resistance of the digital potentiometer 405 (Rg).

The non-inverting input of the operational amplifier 425 is electricallycoupled to the output of the voltage divider formed by the resistor 410(R1) and the resistor 415 (R2). The output of the operational amplifier425 is electrically coupled to an output 435 of the voltage adjustmentcircuit 400. Thus, by combining equations 5 and 6, the voltage gainV_Gain of the voltage adjustment circuit 400 is

V_Gain=V_Out/V_In=(R_2/[R_1+R_2])×(1+[R_f/R_g])   (Equation 7)

where

-   -   V_Out=voltage at the output 435 of the voltage adjustment        circuit 400,    -   V_In=voltage at the input 417 of the voltage adjustment circuit        400,    -   R_1=resistance of the resistor 410 (R1),    -   R_2=resistance of the resistor 415 (R2),    -   R_f=resistance of the resistor 430 (Rf), and    -   R_g=resistance of the digital potentiometer 405 (Rg).

In some embodiments, the voltage gain of the voltage adjustment circuit250 is set to compensate for variations in the voltage ratio of thevoltage divider circuit 215. Alternatively or in addition, the voltagegain of the voltage adjustment circuit 250 is set to compensate forvariations in the voltage ratio of the capacitive voltage dividernetwork formed by the voltage divider circuit 215 and the capacitor 245(C3) in the junction circuit 220. Alternatively or in addition, thevoltage gain of the voltage adjustment circuit 250 is set based on atemperature of the junction circuit 220, a temperature of the voltagedivider circuit 215, or both. For example, in some embodiments, thejunction circuit 220 includes a temperature sensor and sets the voltagegain of the voltage adjustment circuit 250 based on the temperature ofthe junction circuit 220, the temperature of the voltage divider circuit215, or both.

The voltage measurement system 200 can be used with switchgear.Switchgear is the combination of electrical disconnect switches, fuses,and/or circuit breakers and other components used to control, protect,and isolate electrical equipment in electrical power systems. Reclosers(also known as automatic circuit reclosers or autoreclosers) are a classof switchgear designed for use on overhead electricity distributionnetworks to detect and interrupt momentary faults. Reclosers aredesigned to operate with single phase and three phase power distributionnetworks.

FIG. 5 is a diagram of a switchgear system 500 including a recloser 505,according to some embodiments. In the example provided in FIG. 5, therecloser 505 receives high voltage electrical power via a lineconnection 510, and delivers the high voltage electrical power via aload connection 515. An interrupting medium 520 (for example, a vacuuminterrupter) is electrically coupled between the line connection 510 andthe load connection 515 to selectively interrupt current flowtherebetween. Voltage at the line connection 510 is monitored by a firstvoltage sensor 525, and voltage at the load connection 515 is monitoredby a second voltage sensor 530. The switchgear system 500 also includesa junction board 535 that is electrically coupled to the first andsecond voltage sensors 525 and 530. Also shown in FIG. 5 is a reclosercontroller 540 that is electrically coupled to the junction board 535via a control cable 545.

The recloser 505 in FIG. 5 represents one phase of a three phaserecloser. For ease of description, the other two phases of the threephase recloser are not shown or described in detail. However, the othertwo phases of the three phase recloser may include similar components asthe recloser 505 shown in FIG. 5. For example, each of the other twophases may include a recloser interrupting medium, line and loadconnections, and on or two voltage sensors. In some embodiments, a threephase recloser includes two voltage sensors for each phase (i.e., atotal of six voltage sensors). In some embodiments, the junction board535 in FIG. 5 is also electrically coupled to the four voltage sensorsin the other two phases (i.e., a total of six voltage sensors).

FIG. 6 is a diagram of one example embodiment of a voltage sensor 600used for monitoring voltage in a power system. The voltage sensor 600 inFIG. 6 includes a ground reference 605, a high voltage (HV) electrode610, a voltage screen 615, and dielectric material 620. In someembodiments, the ground reference 605, the HV electrode 610, and/or thevoltage screen 615 are cylindrical. Components of the voltage sensor 600in FIG. 6 correspond with components of the voltage divider circuit 215in FIG. 2. For example, the capacitor 230 (C1) represents thecapacitance between the HV electrode 610 and the voltage screen 615, andthe capacitor 235 (C2) represents the capacitance between the voltagescreen 615 and the ground reference 605. Thus, the voltage sensor 600implements a voltage divider. In some embodiments, the voltage level ofthe ground reference 605 is held at earth ground.

Voltage sensors used in reclosers are designed to yield a target voltageratio between the input voltage and the output voltage. For example, avoltage sensor may be designed to yield a target voltage ratio of 10,000to 1. However, due to variations in physical layout and electricalcharacteristics of passive components included in the voltage sensor,the actual voltage ratio of the voltage sensor may vary from the targetvoltage ratio. In some present systems, a recloser controller applies aratio correction factor to scale the output voltage for an accuratereading. As the ratio correction factor is unique to each voltagesensor, ratio correction factors are presently determined by testingeach voltage sensor with a high voltage input to determine a ratiocorrection factor based on the voltage ratio of applied voltage input tomeasured voltage output. The ratio correction factors are provided toend users who must program the ratio correction factors into a reclosercontroller to make the corrections. Reclosers often need to be replaced.For example, reclosers may need to be replaced due to damage caused bylightning strikes or wildlife interference. Additionally, reclosers needto be replaced at their end of life or for equipment upgrades. Thus, thepresent method presents problems for the end users as new correctionfactors must be determined and programmed into a recloser controllereach time a recloser (or a component of a recloser) is replaced.

To remove the need for a ratio correction factor, the junction board 535in FIG. 5 includes the junction circuit 220 of FIG. 2. By setting thevoltage gain of the voltage adjustment circuit 250, the junction circuit220 adjusts the voltage ratio of the voltage divider to implement atarget voltage ratio. As such, the recloser controller 540 does not needto apply a ratio correction factor to the readings of the voltagemeasurement circuit 225. In some embodiments, the ratio correctionfactor of the recloser controller 540 is equal to one (i.e., therecloser controller 540 effectively provides no ratio correctionfactor). The ratio correction factor of the recloser controller 540 maybe set to one by default. Alternatively or in addition, a ratiocorrection factor of one may be programmed into the recloser controller540, for example, by a user.

In some present systems, a true ratio (also known as a nameplate ratio)is programed into a recloser controller instead of a ratio correctionfactor. The true ratio indicates the actual voltage ratio provided by avoltage sensor system. For example, in a present system that provides anactual voltage ratio of 9,921 to one, the true ratio in the reclosercontroller is set to 9,921 to one. The junction circuit 220 of FIG. 2included in the junction board 535 in FIG. 5 also removes the need for atrue ratio adjustment (or true ratio programming). By setting thevoltage gain of the voltage adjustment circuit 250, the junction circuit220 adjusts the voltage ratio of the voltage divider to implement atarget voltage ratio. As such, the recloser controller 540 does not needto apply a true ratio to the readings of the voltage measurement circuit225. In some embodiments, the true ratio of the recloser controller 540is set to the target voltage ratio (i.e., the recloser controller 540effectively provides no true ratio). For example, when the targetvoltage ratio is 10,000 to one and the voltage divider provides anactual voltage ratio of 9,921 to one, the true ratio of the reclosercontroller 540 may be set (by default or via user programming) to 10,000to one because of the voltage gain provided by the voltage adjustmentcircuit 250.

FIG. 7 is a block diagram of one example embodiment of the reclosercontroller 540. The recloser controller 540 in FIG. 7 includes thevoltage measurement circuit 225 of FIG. 2. In addition to the controlresistor 255 (R Control), the voltage measurement circuit 225 in FIG. 7includes an analog-to-digital (A/D) converter 705, a first input 710electrically coupled to the output of the voltage adjustment circuit250, and a second input 715 electrically coupled to the referenceterminal 205. In some embodiments, the first input 710 is electricallycoupled to the output of the voltage adjustment circuit 250 via one ormore other components within the junction circuit 220. The reclosercontroller 540 in FIG. 7 also includes an electronic processor 720 (forexample, a microprocessor), memory 725, a communication interface 730, auser interface 735, and bus 740. The bus 740 connects various componentsof the recloser controller 540, for example, the memory 725 to theelectronic processor 720.

The memory 725 includes read-only memory (ROM), random access memory(RAM), electrically erasable programmable read-only memory (EEPROM),other non-transitory computer-readable media, or a combination thereof.The electronic processor 720 is configured to retrieve programinstructions and data from the memory 725 and execute, among otherthings, program instructions to perform the methods described herein.The memory 725 may store program instructions for operating theinterrupting medium 520. The memory 725 may also store data representinglow voltage voltmeter readings from the voltage measurement circuit 225.

The memory 725 may also store program instructions for estimating thevoltage between the HV electrode 610 and the ground reference 605 basedon low voltage measurements from the voltage measurement circuit 225.The memory 725 may also store data representing estimations of thevoltage between the HV electrode 610 and the ground reference 605. Thememory 725 may also store data representing a ratio correction factor.The memory 725 may also store data representing configuration parametersand program instructions for compensating or calibrating for anyinaccuracies of the magnitude or phase of a voltage reading.

The communication interface 730 includes routines for transferringinformation between components within the recloser controller 540 andother components of the switchgear system 500, as well as componentsexternal to the switchgear system 500. The communication interface 730is configured to transmit and receive signals via wires, fiber,wirelessly, or a combination thereof. Signals may include, for example,information, data, serial data, data packets, analog signals, or acombination thereof.

The user interface 735 is included to control the recloser controller540 or the operation of a switchgear system 500 as a whole. The userinterface 735 is operably coupled to the electronic processor 720 tocontrol, for example, the state of the interrupting medium 520. The userinterface 735 displays visual output generated by software applicationsexecuted by the electronic processor 720. Some examples of visual outputare graphical indicators, lights, colors, text, images, and graphicaluser interfaces (GUIs). The user interface 735 includes a suitabledisplay mechanism for displaying visual output (for example, alight-emitting diode (LED) screen, a liquid crystal display (LCD)screen, or an organic LED (OLED) screen). In some embodiments, the userinterface 735 includes a touch sensitive interface (for example, atouch-screen display). The touch-screen display receives user inputusing detected physical contact (for example, detected capacitance orresistance). Based on the user input, the touch-screen display outputssignals to the electronic processor 720 which indicate positions on thetouch-screen display currently being selected by physical contact.Alternatively or in addition, the user interface 735 receives user inputfrom input devices, for example, knobs, dials, switches, buttons, andkeypads.

Various configurations of the components of the recloser controller 540may be implemented. For example, the voltage measurement circuit 225 maybe integrated with the recloser controller 540 in a single housing, ormay by electrically coupled to the recloser controller 540 but housed ina separate housing. In some embodiments, the voltage measurement circuit225 and/or the recloser controller 540 may be positioned near to theinterrupting medium 520, for example, near the junction board 535 or atsome other location that is more accessible by a user.

FIG. 8 is a diagram of an example embodiment of a switchgear system 800for calibrating a recloser voltage measurement system. In the exampleshown in FIG. 8, the switchgear system 800 includes the recloser 505,the junction board 535, the recloser controller 540 described previouslyherein. The line connection 510 of the recloser 505 is electricallycoupled to a high voltage connection 805 to receive a high voltage (forexample, voltages from 2,400 volts to 100 kilovolts). The switchgearsystem 800 in FIG. 8 also includes a voltage divider 810, a digitalmultimeter 815, and a calibration controller 820. The voltage divider810 is electrically coupled to the high voltage connection 805 toprovide a low voltage output proportional to the applied high voltage.The voltage divider 810 may include a reference voltage dividercalibrated to provide an actual voltage ratio that is equal (or veryclose) to a target voltage ratio. The digital multimeter 815 (forexample, the 34410A Digital Multimeter by Agilent Technologies) iselectrically coupled to the voltage divider 810 to read the low voltageoutput. The calibration controller 820 is electrically coupled to thedigital multimeter 815 to receive readings of the low voltage output.The calibration controller 820 is also electrically coupled to therecloser controller 540 to receive voltage measurements of the output ofthe junction circuit 220 in the junction board 535. The calibrationcontroller 820 is further electrically coupled to the voltage adjustmentcircuit 250 in the junction circuit 220 (which is located in thejunction board 535). The calibration controller 820 is configured tosend control signals to the voltage adjustment circuit 250 which causethe voltage adjustment circuit 250 to set a target voltage gain. In someembodiments, the calibration controller 820 includes components orcombinations of different components, including all or some of thevarious components described above with respect to the reclosercontroller 540. For example, the calibration controller 820 may includean electronic processor, memory, a communication interface, a userinterface, specialized software, or a combination thereof. In someembodiments, the calibration controller 820 includes a laptop, adesktop, a tablet, a server, or a combination thereof.

FIG. 9 is a flow chart of a method 900 for calibrating a recloservoltage measurement system, according to some embodiments. For ease ofdescription, the method 900 is described in terms of calibrating thevoltage adjustment circuit 250 when it is electrically coupled to thefirst voltage sensor 525 of the recloser 505. The same (or a similar)method may also be used to calibrate a voltage adjustment circuit thatis electrically coupled to the second voltage sensor 530 of the recloser505, or any other voltage sensor included in the recloser 505.

At block 905, a first voltage measurement at a high voltage input to therecloser 505 is determined. In some embodiments, the high voltage inputis the line connection 510 of the recloser 505. For example, thecalibration controller 820 may receive a reading from the digitalmultimeter 815 of the low voltage output produced by the voltage divider810. This reading of the low voltage output is proportional to theapplied high voltage at the high voltage connection 805. As the lineconnection 510 of the recloser 505 is also electrically coupled to thehigh voltage connection 805, this reading of the low voltage output isrepresentative of the actual value of high voltage applied to the lineconnection 510 of the recloser 505. Thus, in some embodiments, the firstvoltage measurement represents the actual value of high voltage appliedto the line connection 510 of the recloser 505, as seen through thevoltage divider prior to setting the ratio correction factors. Inalternate embodiments, the high voltage input is the load connection 515of the recloser 505, and the first voltage measurement represents theactual value of high voltage applied to the load connection 515 of therecloser 505. In some embodiments, the high voltage can be applied tothe load connection 515 and the line connection 510 simultaneously.

At block 910, a second voltage measurement at the output of the voltageadjustment circuit 250 is determined. For example, the calibrationcontroller 820 may receive a signal from the recloser controller 540indicating a voltage reading of the output of the voltage adjustmentcircuit 250 taken by the voltage measurement circuit 225. In someembodiments, the second voltage measurement represents an (uncalibrated)measurement of the high voltage applied to the line connection 510 ofthe recloser 505 taken by the voltage measurement system 200.

At block 915, a difference between the first and second voltagemeasurements is calculated (for example, by the calibration controller820). This difference represents the measurement error of the voltagemeasurement system 200. For example, the voltage measurement system 200may be designed such that voltage divider formed by the first voltagesensor 525 (and the capacitor 245 (C3) in the junction circuit 220)provides a voltage ratio of 10,000 to 1. However, due to the processvariations of the components of the first voltage sensor 525 (and thecapacitor 245 (C3) in the junction circuit 220), this voltage dividermay actually provide a voltage ratio of 10,000 to 1.035. Thus, when10,000 volts is applied to the line connection 510 of the recloser 505,the first voltage measurement (measured, for example, by the voltagedivider 810) would be 10,000 volts and the second voltage measurement(measured, for example, by the voltage measurement system 200) wouldindicate 10,350 volts. The 350 volt difference between the first andsecond voltage measurements represents the error in the voltagemeasurement.

At block 920, a target voltage gain for the voltage adjustment circuit250 is determined based on the difference between the first and secondvoltage measurements. As described above, the difference between thefirst and second voltage measurements represents, among other things,the variation in the voltage ratio of the voltage divider circuit 215.Thus, the calibration controller 820 may determine a target voltage gainfor the voltage adjustment circuit 250 that offsets this variation. Insome embodiments, the calibration controller 820 determines the targetvoltage gain VT_Gain for the voltage adjustment circuit 250 as

VT_Gain=V_Out/V_In=1+([VM1−VM2]/VM1)   (Equation 8)

where

-   -   V_Out=output voltage of the voltage adjustment circuit 250,    -   V_In=input voltage of the voltage adjustment circuit 250,    -   VM1=first voltage measurement, and    -   VM2=second voltage measurement.

For example, when the first and second voltage measurements are 10,000volts and 10,350 volts, respectively, the calibration controller 820 maydetermine a target voltage gain of 0.965 for the voltage adjustmentcircuit 250 (i.e., 1+([10,000−10,350]/10,000)).

At block 925, the voltage ratio of the voltage divider is adjusted bysetting the voltage adjustment circuit 250 to the target voltage gain.In some embodiments, the voltage adjustment circuit 250 is set to thetarget voltage gain by setting a resistance of a dip-switch resistorarray included in some embodiments of the voltage adjustment circuit250. For example, with reference to the voltage adjustment circuit 300in FIG. 3, the calibration controller 820 may determine a target closedloop gain for the operational amplifier 325 such that the voltage gainof the voltage adjustment circuit 300 is set to the target voltage gain.The calibration controller 820 may then determine a target resistancefor the dip-switch resistor array 305 such that the closed loop gain ofthe operational amplifier 325 is set to the target closed loop gain. Thecalibration controller 820 may then determine a configuration of thethree switches SW1, SW2, and SW3 such that the resistance across thedip-switch resistor array 305 is set to the target resistance. Forexample, when the target resistance is equal to the combined seriesresistances of the resistor Rf1 and the resistor Rf3, the calibrationcontroller 820 may determine that the switches SW1 and SW3 should be inthe open position and the switch SW2 should be in the closed position.In some embodiments, the calibration controller 820 presents thedetermined configuration of the switches SW1, SW2, and SW3 to a user.For example, the calibration controller 820 may display the determinedconfiguration of the switches SW1, SW2, and SW3 to a user on a displayscreen included in some embodiments of the calibration controller 820.

In alternate embodiments, the voltage adjustment circuit 250 is set tothe target voltage gain by setting a resistance of a digitalpotentiometer included in some embodiments of the voltage adjustmentcircuit 250. For example, with reference to the voltage adjustmentcircuit 400 in FIG. 4, the calibration controller 820 may determine atarget closed loop gain for the operational amplifier 425 such that thevoltage gain of the voltage adjustment circuit 400 is set to the targetvoltage gain. The calibration controller 820 may then determine a targetresistance for the digital potentiometer 405 such that the closed loopgain of the operational amplifier 425 is set to the target closed loopgain. The calibration controller 820 may then send a control signal tothe digital potentiometer 405 which causes the digital potentiometer 405to set its resistance to the target resistance.

In some embodiments, the recloser controller 540 may perform all (or anyportion) of the method 900 described above. For example, the reclosercontroller 540 may be configured to determine the target voltage gainand set the voltage adjustment circuit 250 to the target voltage gain.

In the foregoing specification, specific embodiments have beendescribed. However, one of ordinary skill in the art appreciates thatvarious modifications and changes can be made without departing from thescope of the invention as set forth in the claims below. Accordingly,the specification and figures are to be regarded in an illustrativerather than a restrictive sense, and all such modifications are intendedto be included within the scope of present teachings.

The phrase “electrically coupled in series” as used herein refers to acircuit arrangement in which the described elements are arranged, ingeneral, in a sequential fashion such that the output of one element iselectrically coupled to the input of another, though the same currentmay not pass through each element. For example, additional circuitelements may be electrically coupled in parallel with one or more of theelements “electrically coupled in series.” Furthermore, additionalcircuit elements can be electrically connected in series at nodes suchthat branches in the circuit are present. Therefore, elementselectrically coupled in series do not necessarily form a true seriescircuit.

Additionally, the phrase “electrically coupled in parallel” as usedherein refers to a circuit arrangement in which the described elementsare arranged, in general, in a manner such that one element iselectrically coupled to another element, such that the circuit forms aparallel branch of the circuit arrangement. In such a configuration, theindividual elements of the circuit may not have the same potentialdifference across them individually. For example, in a parallel-typeconfiguration of the circuit, two circuit elements electrically coupledin parallel with one another may be electrically coupled in series withone or more additional elements of the circuit. Therefore, elementselectrically coupled in parallel do not necessarily individually form atrue parallel circuit.

It will be appreciated that some embodiments may be comprised of one ormore generic or specialized processors (or “processing devices”), forexample, microprocessors, digital signal processors, customizedprocessors and field programmable gate arrays (FPGAs) and unique storedprogram instructions (including both software and firmware) that controlthe one or more processors to implement, in conjunction with certainnon-processor circuits, some, most, or all of the functions of themethod and/or apparatus described herein. Alternatively, some or allfunctions could be implemented by a state machine that has no storedprogram instructions, or in one or more application specific integratedcircuits (ASICs), in which each function or some combinations of certainof the functions are implemented as custom logic. Of course, acombination of the two approaches could be used.

Moreover, an embodiment can be implemented as a computer-readablestorage medium having computer readable code stored thereon forprogramming a computer (for example, comprising an electronic processor)to perform a method as described and claimed herein. Examples of suchcomputer-readable storage mediums include, but are not limited to, ahard disk, a CD-ROM, an optical storage device, a magnetic storagedevice, a ROM, a programmable read-only memory (PROM), an EEPROM, anerasable programmable read-only memory (EPROM), and a Flash memory.

Various features and advantages are set forth in the following claims.

We claim:
 1. A junction circuit electrically coupled to an output of acapacitive voltage divider circuit, the junction circuit comprising: acapacitor electrically coupled between the output of the capacitivevoltage divider circuit and a reference terminal; and a voltageadjustment circuit electrically coupled between the output of thecapacitive voltage divider circuit and an output of the junctioncircuit, the voltage adjustment circuit including an adjustableimpedance component configured to adjust a voltage gain of the voltageadjustment circuit.
 2. The junction circuit of claim 1, wherein theadjustable impedance component includes a dip-switch resistor array. 3.The junction circuit of claim 1, wherein the adjustable impedancecomponent includes a digital potentiometer.
 4. The junction circuit ofclaim 3, wherein the digital potentiometer is configured to receive acontrol signal, and set a resistance of the digital potentiometer basedon the control signal.
 5. The junction circuit of claim 4, wherein thecontrol signal is determined based on a voltage measured at the outputof the junction circuit.
 6. The junction circuit of claim 1, wherein thejunction circuit is configured to measure a temperature of at least oneselected from a group consisting of the junction circuit and thecapacitive voltage divider circuit, and set the voltage gain of thevoltage adjustment circuit based on the temperature.
 7. A switchgearsystem comprising: a switchgear device; a voltage divider circuitincluding an output and an input electrically coupled to the switchgeardevice; and a junction circuit including an input electrically coupledto the output of the voltage divider circuit, a voltage adjustmentcircuit configured to adjust a voltage ratio of the voltage dividercircuit, and an output electrically coupleable to a voltage measurementcircuit.
 8. The switchgear system of claim 7, wherein the switchgeardevice includes a three phase recloser, and wherein the input of thevoltage divider circuit is electrically coupled to a line connection ofone phase of the three phase recloser.
 9. The switchgear system of claim7, wherein the switchgear device includes a recloser, and wherein thevoltage measurement circuit is included in a recloser controller. 10.The switchgear system of claim 7, wherein the voltage adjustment circuitincludes a dip-switch resistor array configured to adjust a voltage gainof the voltage adjustment circuit.
 11. The switchgear system of claim 7,wherein the voltage adjustment circuit includes a digital potentiometerconfigured to adjust a voltage gain of the voltage adjustment circuit.12. The switchgear system of claim 11, wherein the digital potentiometeris configured to receive a control signal, and set a resistance of thedigital potentiometer based on the control signal.
 13. The switchgearsystem of claim 12, wherein the control signal is determined based on avoltage measured by the voltage measurement circuit.
 14. The switchgearsystem of claim 7, wherein the voltage divider circuit includes acapacitive voltage divider network.
 15. The switchgear system of claim14, wherein a first capacitor of the junction circuit is electricallycoupled in parallel to a second capacitor of the capacitive voltagedivider network.
 16. The switchgear system of claim 15, wherein thevoltage adjustment circuit is electrically coupled in series with thefirst capacitor.
 17. A method of calibrating a recloser voltagemeasurement system, the recloser voltage measurement system including avoltage divider electrically coupled to a recloser and a voltageadjustment circuit including an input electrically coupled to an outputof the voltage divider, the method comprising: determining a firstvoltage measurement at a high voltage input to the recloser; determininga second voltage measurement at an output of the voltage adjustmentcircuit; calculating a difference between the first voltage measurementand the second voltage measurement; determining a target voltage gainbased on the difference between the first voltage measurement and thesecond voltage measurement; and adjusting a voltage ratio of the voltagedivider by setting the voltage adjustment circuit to the target voltagegain.
 18. The method of claim 17, wherein the recloser voltagemeasurement system further includes a recloser controller electricallycoupled to an output of the voltage adjustment circuit, and wherein aratio correction factor of the recloser controller is equal to one. 19.The method of claim 17, wherein the voltage adjustment circuit includesa dip-switch resistor array, and wherein setting the voltage adjustmentcircuit to the target voltage gain includes setting a resistance of thedip-switch resistor array based on the target voltage gain.
 20. Themethod of claim 17, wherein the voltage adjustment circuit includes adigital potentiometer, and wherein setting the voltage adjustmentcircuit to the target voltage gain includes determining a targetresistance based on the target voltage gain, and sending a controlsignal to the digital potentiometer to set the digital potentiometer tothe target resistance.